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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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462
ALASKAN GLACIER STUDIES
SECTIONS or FINE GLACIAL OTJTWASH DEPOSITS AT WBSTEBN BBIDGE ACROSS FLAG
POINT CHANNEL
Material	Thickness	Material	Thickness	Material	Thickness
Sand and gravel	18				
Sand	4				
Sand and gravel	4				
Unrecorded	6				
Fine sand	*	Glacial mud	4	Glacial mud	7
(Sea level)		(Sea level)		(Sea level)	
Fine gravel	7	Fine sand	15	Fine sand and	
				gravel	18*
Coarse gravel	17	Sand and gravel	18	Coarse sand and	
				gravel	16
SUt and vegetation	18	Gravel	11	SUt and vege-	
				tation	8
Gravel	2			Sand and	
				gravel	2
Sand	12				
The first point concerning these sections is that they show moderate-sized material, compared with the bowldery outwash, shown in the section (p. 461), 20 miles to the north at Miles Glacier bridge.
The three sections given above are 250 to 850 feet apart and the lack of correspondence of the sand or gravel layers shows the normal horizontal variation common to river deposits.
Eight other borings between this point and Long Island show similar relationships and variations, which indicate that, in the past, there have been the usual differences in velocity and carrying power of this glacial stream, which alternates in depositing sand, gravel and silt. These borings go 50 to 60 feet below sea level, but the total thickness of the glacial deposits of the Copper River delta, is quite unknown. Six miles farther northeast at Hotcake Channel the borings show similar gravel and sand, extending below sea level.
Vegetation Indicating Sinking of the Land. The presence of vegetation in the silt at a depth of 20 to 40 feet below sea level in two of these borings shown in the table and in two others to the eastward shows that the Copper River delta has been subjected to a submergence in recent times, as is the case in parts of Prince William Sound to the westward, as well as 80 miles east near Controller Bay.
In the latter locality E. C. Hawkins states that hi putting down borings, to see if it was possible to support a railway trestle on piles in the shallow Bering Lake, a layer of peat was encountered 80 feet below the surface. As the tide now rises into this lake the depth of this peat layer below sea level is about the same as on the Copper River delta.